Remaining Free Agent Strikeout Relievers

Everyone loves having relievers that can strike batters out in their bullpen, guys that can record outs all by themselves without the help of their defense. That comes in handy when there are men in base, since it's really hard to score without putting the ball in play. Take David Robertson of the Yankees for example; he faced 19 batters with the bases loaded last season and struck out 14 of them. Great way to prevent runs.

The pool of unsigned free agent relievers is at least 30 pitchers deep, but not all of those relievers are strikeout guys. We're going to take a look at those with an affinity for strike three using two metrics: K/9 and K%. You're probably familiar with K/9, which is strikeouts per nine innings. The league average was 7.13 K/9 in 2011, and Kenley Jansen led all qualified relievers with 16.10 K/9. The second metric, K%, is simply the percentage of batters faced that the pitcher struck out. It's a more accurate measure of strikeout proficiency. The league average was 18.6% in 2011, and Jansen again led all qualified relievers at 44.0%.

As you'll see below, the K/9 and K% leaderboards are similar but not identical. More efficient pitchers will have a higher K%, even though they may have a lower K/9 than their baserunner-prone counterparts. Here are lists of unsigned free agent relievers with above average K/9 and K% rates.

Dan Wheeler just missed the cut with a 7.11 K/9. He would have posted an above average 7.30 K/9 with just one more strikeout last year, and I'm sure an umpire robbed him of a strike three call somewhere along the line. Free agent closer Francisco Cordero struck out a well below average 5.43 batters per nine innings last year.

Strikeouts Per Batters Faced (K%)

Wood – 25.5%

Madson – 25.2%

Cruz – 23.0%

Gonzalez – 22.2%

Wuertz – 19.8%

Wheeler – 19.4%

Durbin – 18.6%

Rodney (17.3%) drops off the list in favor of Wheeler, which essentially means that more of the outs he recorded were strikeouts, but Wheeler was more efficient and struck out a higher percentage of the batters he faced. Make sense? Cordero was again well below average at 15.3%.

the problem being that strikeout proficiency, per se, is itself not a great indicator of ability to prevent runs – which is the main thing. It’s better to think of K rates as thresholds, rather than some kind of linear correlation with actual effectiveness. Most people know the 4.5/9ip “threshold” but you really get a either diminishing returns for rates above 7.75/9 or at the very top, as both sets of numbers illustrate, you’re going to have problems with sample size (i.e. so few people have the very top rates, you’re really not measuring more than how good or bad a few pitcher’s years were). using K% v. K/9 is *probably* a better measure, but I think there is some discussion as to whether walks at the higher levels are or are not an indication of a proficiency “problem” – that is, for most pitchers, high K rates might even necessitate higher than average walk rates, so measuring K’s against batters faced might distort the way high K-rates are actually generated. Th lists are, in any case very similar top to bottom (if you don’t slice the list at some abitrary point) and the correlation to run prevention is variable enough that the changes in positions between the two lists (all fairly similar) wouldn’t necessarily indicate any actual performance difference in run prevention. It *might* be better to express the number as /9ip even if it is less precise if the number was more easily digested or was closer in its expression to real life events. i.e. in the k/9 the difference ebtween an 8 and a 9 is a K per game. What exactly is the difference between 15.3% and 17.3%? over a game? over a typical season? ( five or six baserunners? how many fewer K’s?) It’s not that we couldn’t as a group of readers *learn* what is good or bad over time, but is the difference enough to justify going away from something that is already expressed in an identifiable way?